To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The full-dimension (FD)-multi-input multi-output (MIMO) system is also referred to as a high-capacity MIMO system. The high-capacity MIMO communication system mostly assumes a time division duplexing (TDD) system out of a frequency division duplexing (FDD) scheme and the TDD scheme, and utilizes the channel reciprocity of an uplink and a downlink, so as to avoid the issue associated with a channel feedback. However, the FDD scheme is still broadly utilized in many cellular networks, and actually, applying the high-capacity MIMO technology to the FDD system is an important issue, from the perspective of backward compatibility. To perform beamforming in a transmitting node of the FDD system, channel state information is required. However, it is difficult to use the uplink resources only for the purpose of feedback of the channel state information, and thus, the channel feedback is generally expressed as a limited number of feedback bits. When the feedback information is incomplete information, the beamforming of the transmitting node is also incorrect. Actually, in the case of multi-user (MU)-MIMO system, due to the incorrect beamforming, inter-user interference may be incompletely removed and thus, a signal-to-interference-and-noise ratio (SINR) of a receiving node may deteriorate. It is an interference-limited system under the limited feedback, and thus, the accuracy of the channel state information may directly affect a multiplexing gain of a MU-MIMO downlink. Particularly, to maintain the difference with the sum rate of complete channel state information within a predetermined range, the number of bits for quantizing a channel needs to be set to be proportional to the number of base station's antennas and a signal-to-noise ratio (SNR). In addition, the FD-MIMO system is a technology in which a base station obtains a high transmission rate by utilizing a large number of (tens to hundreds of) antennas, and the feedback load that simply increases in proportion to the number of antennas may continuously increase.